Sliding contact of or between elements constituting a reservoir, seals intended to close the interface between revolving shafts on which agitator blades are mounted and reservoirs wherein such blades operate (such as crystallizers), and seals of piston rods, valves and stopcocks, have always been points where liquid leakage and the problems it entails are expected to occur due to excessive wear and change in acceptable tolerances.
Prevention of liquid leakage at these points have been difficult to overcome. For example, since end plates provided at the both ends of top-fed double drum dryers, used for drying various solutions such as food concentrates, are positioned in such a manner that the drums rotate in sliding contact with the end plates, the sliding contact sections will invariably develop unacceptable tolerances, where, leakage of liquid becomes unavoidable. The same can be said for the end plates of a roller coater to apply adhesives or paints, or those of a transfer roller for printing inks. Further, adequate tolerances are necessary to assure smooth rotation or movement of revolving shafts, agitator blades and sliding rods mounted on various vessels. The provision of packings at these points has prevented leakage of liquid satisfactorily due to packing wear.